1. Field of the Invention
The present invention relates to a method and process for strengthening and stiffening tubes and pipes using internal stiffening elements which are welded after such elements achieve their final form and position with in the tube. In particular, the method is especially suitable for strengthening tubes with different cross sections along their length, or bent or helically formed tubes.
2. Background of the Prior Art
Except for extruded light-metal products, no method or process for internally strengthening tubes with different cross-sections along their length or tubes with bends or spirals, while allowing for reductions in tube wall thickness and/or tube weight, is known. No process for bending or otherwise forming tubes with stiffening elements already in place is known.
The following methods of joining elements and partitions within a tube by use of heat or adhesives are known: (1) painting of a soldering mixture on the parts to be joined, followed by heating of the parts in a reducing atmosphere (Noble, GB- No. 484,455), (2) welding by use of a binding material in wire form inserted into the tube, after which the tube is heated in a reducing atmosphere to the melting point of the binding material (Gillette et al, U.S. Pat. No. 1,472,518), and the brazing of the edges of the strengthening element near each end of the tube for a slight distance (Passmore, U.S. Pat. No. 908,127). In the present invention, one of the preferred methods of welding the strengthening elements in the tube, that of induction warming of the joints which have pre-formed welding or soldering material firmly attached to the strengthening element or forming an integral part thereof, in the presence of the normal atmosphere, is not known from the prior art.